Apparatus for bioprocessing a circulating fluid

ABSTRACT

The invention relates to the safe and effective biotreatment of circulating fluids. In one general aspect of the invention, an apparatus (e.g., liver assist system) for circulating and bioprocessing a fluid (e.g., plasma) includes a conduit for circulating the fluid, an oxygenator for supplying oxygen to the fluid, a pump adapted to circulate the fluid through the conduit, a bioreactor unit, connected within the conduit, adapted to process the fluid, and a container connected within the conduit for receiving and releasing a portion of the fluid.

BACKGROUND OF THE INVENTION

There is a need for apparatuses which safely and effectively bioprocessa circulating a body fluid, such as whole blood or plasma. As anexample, the development of liver support apparatuses has progressedfrom passive or removal systems to bioactive or biochemical systems. Thepassive systems have included hemodialysis, hemoperfusion, plasmaexchanges, etc. for removing the blood toxins which accumulate duringliver failure.

The successful reports of orthotopic liver transplantation in prolonginglife has led to the conceptual development of biochemical or cell basedliver support systems. These systems consist mainly of bioreactorscontaining cells. For example, a bioartificial liver device may includea hollow fiber cartridge containing primary pig liver cells. The livercells are seeded in the extra-capillary space of the hollow fibers, andblood or plasma is perfused through the lumen of the fibers. Microporoushollow fibers permit passage of plasma proteins but prevent the passageof cells (e.g., blood cells and liver cells), thereby allowing thetransport of soluble and protein-bound substances from the plasma acrossthe hollow fiber walls and into the space occupied by the porcinehepatocytes.

SUMMARY OF THE INVENTION

This present invention relates to bio-treatment of circulating fluids. Ageneral aspect of the invention involves an apparatus (e.g., liverassist system) for circulating and bioprocessing a fluid (e.g., plasmaor lymph fluid) which includes a conduit for circulating the fluid, anoxygenator connected within the conduit for supplying oxygen to thefluid, a pump adapted to circulate the fluid through the conduit, abioreactor unit connected within the conduit for processing the fluid,and a container also connected within the conduit for receiving andreleasing a portion of the fluid. If desired, a charcoal filter can alsobe added to the apparatus of this invention for pre-filtering the fluidbefore it is bio-treated in the bioreactor unit.

The apparatus may include an in-port for receiving fluid from anexternal system (e.g., a plasma separation machine or a patient) and anout-port for returning the fluid to the external system. When used insuch a manner, the apparatus is said to be operated as an open system.In this on-line arrangement, it is generally preferred that the fluid bereceived and treated by the bioreactor unit prior to being received atthe container in order to avoid unnecessary dilution of the fresh fluid.In an open-system operation, it is preferred that the apparatus includebypass structure, which upon actuation, prevents flow of the fluidbetween the conduit and the external system. The bypass structure allowsthe apparatus to be isolated from the external system in the event of anemergency or to be simply detached and allowed to operate independently.

Alternatively, the apparatus may be used independently as a closedsystem. In a closed operation, the container itself may serve as thesource of the fluid to be treated by the apparatus, or a separatecontainer may be attached to the in-port of the apparatus to supply anuntreated fluid.

The apparatus may include a heater for maintaining the fluid within atemperature range or may be placed in a temperature-controlledenvironment (e.g., heated room) which maintains the temperature of thefluid. Preferably, the oxygenator and heater are provided as an integralunit.

In an embodiment of the apparatus, the container includes a firstcompartment configured to receive the fluid into the container throughan inlet disposed in the first compartment, and a second compartmentconfigured to receive fluid overflowing from the first compartment andto allow flow of the fluid out of the container through an outletdisposed in the second compartment. The container is multifunctional.The inlet and outlet are configured within the compartments to provide areservoir to serve as a buffer to compensate for fluctuations in theflow rate of the fluid (i.e., surges). The container is preferably sizedto have a sufficient cross-sectional area with respect to thecross-sectional area of the conduit to reduce the velocity of the fluidentering the container. Moreover, the container, when made of atransparent material, provides a window for monitoring, either visuallyor electronically, the volume of the fluid within the apparatus. Theflow rate of the fluid entering the apparatus can then be adjusted basedon volume changes, if necessary. Further, the inlet and outlet can bepositioned with respect each other so that particulate matter (e.g.,fibrins)--which can cause clogging within the conduit and the componentsdisposed therein (i.e., oxygenator, filters, bioreactor)--aresubstantially prevented from being released from the container. Inaddition, the compartments may be physically separated by a dividingelement with the particulate matter trapped within the compartmentassociated with the inlet. The container may include additionalcompartments between the compartments associated with the inlet andoutlet. In this arrangement, the fluid successively overflows from onecompartment to the next until reaching the outlet.

The container may include a vent to allow the escape of gas in the formof bubbles. Bubbles which collect within the oxygenator, charcoal filterand bioreactor unit of the apparatus can reduce the effectiveness ofthese components in performing their respective functions.

The apparatus may be used in conjunction with a cell inoculation deviceconnected to a second in-port of the apparatus. The cell inoculationdevice inoculates (or seeds) cells into the bioreactor unit of theapparatus. The cell inoculation system includes: a receptacle with anentrance for receiving cells into an interior volume of the receptacle,a tube extending from an exit of the receptacle configured to allow thewithdrawal of the cells from the interior volume, and a pressuremechanism, attached to the receptacle, for providing a positive pressurewithin the interior volume of the receptacle with respect to theexternal atmosphere of the receptacle. The positive pressure within theinterior volume of the receptacle induces the withdrawal of the cellsfrom the receptacle into the bioreactor unit. The receptacle may includea second inlet configured to introduce a rinsing solution to theinterior volume of the receptacle. The pressure mechanism may include apressure cuff adapted to squeeze a receptacle made of a flexiblematerial. Alternatively, the pressure mechanism may include a source forproviding pressurized gas to the interior volume of the receptacle.

Other features and advantages of the invention will become apparent fromthe following drawings and detailed description, and also from theclaims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a liver assist system accordingto the invention.

FIG. 2 is a plan view of a container adapted to receive and release theprocessed fluid treated within the liver assist system of FIG. 1.

FIG. 3 is a diagrammatic view of a cell inoculation device forinoculating cells into the bioreactor unit of the liver assist system ofFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a schematic representation of a liver assist system5 includes a conduit 6 made of disposable plastic tubing (e.g., PVC) forcirculating plasma through a bioartificial liver (BAL) device 8 whichcontains liver cells. Conduit 6 may include sections of tubing (11, 13,70, 74) used to connect liver assist system 5 to an external system,such as a plasma separation machine 100. Connected within conduit 6, ina series arrangement, are a peristaltic pump 14, optional charcoalfilters 16, 18, an oxygenator/heat exchange unit 20, the BAL device 8,and a reservoir bag 28, each of which will be discussed in greaterdetail below. Liver assist system 5, in use, supports approximately 650ml of fluid with about 120 ml disposed within conduit 6.

Prior to introducing the plasma to liver assist system 5, saline (orother suitable fluid) is used to entirely fill conduit 6 as well as thecomponents of the system. Reservoir bag 28 is also filled sufficientlyto provide a buffer for incoming fluid and indicates when liver assistsystem is entirely filled and primed. This process is part of acleansing process in which the system is rinsed and primed using amethod described below.

In general, plasma is provided to the liver assist system 5 at anin-port 10 via tubing 11 and is pumped through the system using pump 14in the direction indicated by arrows. Filters 16, 18 prefilter theplasma of toxins while oxygenator/heat exchange unit 20 oxygenates andmaintains the temperature of the plasma within a predeterminedtemperature range. The plasma is then received by the BAL device 8 thathas been seeded with liver cells which remove toxins from the plasma.The reservoir bag 28 receives the treated plasma before beingrecirculated back through the system.

Liver assist system 5 is generally used in conjunction with a cellinoculation device 200 (described below) which provides liver cells tothe BAL device. The liver cells remove or modify toxic substances fromthe plasma.

In FIG. 1, liver assist system 5 is shown as part of an on-line systemthat is connected to an external system (e.g., plasma separation machine100) which supplies plasma to the liver assist system for treatment. Theplasma from plasma separation machine 100 is provided to conduit 6 fromtubing 11 and returned from liver assist system 5 via tubing 13.

The plasma separation machine 100 shown in FIG. 1 separates plasma to betreated from whole blood of a human patient. In other on-lineapplications, the external system may be a patient and the whole bloodof the patient is circulated and bioprocessed in liver assist system 5.It is also important to note that liver assist system 5 may be used inan off-line operation in which a source of plasma to be treated isprovided, for example, in a bag and connected to an in-port 10 of theliver assist system 5. In this case, the untreated plasma is allowed tocirculate through the liver assist system to be detoxified and thendispensed at an out-port of the system.

Disposed within the conduit 6 is pump 14, which provide sufficient driveto force the plasma from tubing 11 to flow through the conduit 6 in thedirection indicated by arrows. The plasma flows at a user selectableflow rate between 50 and 1000 ml/min, nominally 400 ml/min. The systemoptionally includes a pair of charcoal filters 16, 18 for pre-filteringthe plasma before it is provided to the BAL device 8. Only one of thefilters is in use at any given time, the other being available to allowcontinued use of the system when one of the filters needs to bereplaced. Clamps (not shown) are used to allow and/or restrict flowthrough one or the other of the filters. Either of the charcoal filters16 or 18 may be replaced with a length of tube 17 or 19 to provide abypass path around the charcoal filter when system 5 is in use.

Plasma from the filters passes to oxygenator/heat exchange unit 20having an oxygenator 22 which supplies oxygen to the plasma and a heater24. Oxygenator 22 receives, at inlet 22a, pressurized sterile gas (e.g.,30% O₂, 5% CO₂, 65% N₂) from an external gas source (not shown). Theplasma passes through semi-permeable hollow fibers disposed within theoxygenator 22 to collect oxygen needed by the liver cells inoculatedwithin BAL device 8. An optional oxygen measurement system may be usedto measure the difference between the oxygen content of the plasmaentering and exiting BAL device 8 to provide an indication of theeffectiveness of the BAL device. The pressurized gas provided to theoxygenator passes through hydrophobic membranes disposed respectively atinlet 22a and outlet 22b.

Plasma flowing through heater 24 is maintained at a predeterminedtemperature (e.g., 37° C.) by heat conduction as it flows past a heatexchanger within the oxygenator. Heated water from an external waterheater/recirculator (not shown) is received at inlet 24a of the heaterand returned via outlet 24b for reheating. A bypass line 25 with a clamp(not shown) is provided to bypass oxygenator/heat exchange unit 20 andthrough the system to allow the cleaning or replacement of theoxygenator/heat exchange unit 20.

Plasma from oxygenator/heat exchange unit 20 is received by thebioartificial liver device 8 (e.g., a replaceable hollow fiber cartridgeinoculated with cells). BAL device 8 includes a bundle of hollow fibers.In one embodiment, the fibers are inoculated with liver cells so thattoxic substances within the plasma are removed as the plasma passesbetween the fibers. Alternatively, the plasma can pass along the axiallength of the fibers with the liver cells introduced between the fibers.A bypass line 26 having a manual clamp is provided to bypass the BALdevice 8, for example, when the BAL device requires replacement,maintenance, or cleansing (described below). During operation of liverassist system 5, tubing 29 attached to waste bags 31, 33 (describedbelow), is closed off from flow of plasma with pinch valve 27.

The treated plasma is then conveyed to the plasma reservoir bag 28before being recirculated through the system with a portion also beingreturned to the plasma separation machine 100. Referring to FIG. 2,reservoir bag 28 is made of a strong and pliable material, such as PVCplastic. Reservoir bag 28 includes an inlet 30 and a pair of outlets 32,34 at the lower end of the bag. Outlet 32 provides fluid back to BALdevice 8 for further treatment, while outlet 34 leads to the plasmaseparation machine 100. A dividing partition 36 between inlet 30 andoutlets 32, 34 define a pair of compartments 38, 40. Compartment 38provides an inlet channel and compartment 40 provides an overflowreservoir for holding a volume (e.g., 100 ml) of fluid. Dividingpartition 36 between compartments 38, 40 ensures that particulate matterwhich may be in the plasma is trapped in compartment 38 and preventedfrom returning to the liver assist system 5 where it may cause cloggingof conduit 6 and the components of the system. Due to the increasedcross-sectional area of compartment 38 (with respect to thecross-sectional area of inlet 30), the velocity of the plasma enteringreservoir bag 28 decreases. Thus, the particulate matter is allowed tosettle in the lower portion of compartment 38. The plasma overflowinginto compartment 40 is temporarily held before being recirculated to theliver assist system 5 or plasma separation system 100. Reservoir bag 28also serves to accommodate surging of the plasma.

Reservoir bag 28 may include multiple compartments between inlet 30 andoutlets 32, 34 so that the particulate matter will settle in the bottomportions of each compartment as the plasma overflows from onecompartment to the next.

A vent 48 is provided at the top of reservoir bag 28 by a tube 50 whichextends to a filter 52 (e.g., 0.2 micron). Vent 48 allows gas within theplasma, in the form of bubbles, to escape.

One approach for forming reservoir bag 28 is to overlay two sheets ofPVC plastic cut in the shape of the bag. RF energy is then applied tothe periphery of the sheets to provide an air-tight edge 42 to the bag.Support seams 44, along the top portion of bag 28, are provided whereholes are punched for allowing the bag to be hung from a support. Anadditional support seam 45 at the side of the bag is provided along oneside of bag 28 so that compartment 40 defines a reservoir of sufficientdepth. Support seams 44 and 45, as well as dividing partition 36, areformed also using the RF heat-sealing technique.

The level of plasma in reservoir bag 28 can be visually observed by theoperator of the system who can manually release or restrict flow of theplasma from the bag to maintain a proper level of plasma in the bag, forexample, using line 15. The level can also be maintained using anelectronic device which controls pump 14 of the liver assist systemand/or a pump of the plasma separation machine 100.

An optional filter 9 with a bypass 12 may be included within tubing 70for filtering particulate matter from the plasma returning to theexternal system. Filter 9 serves to capture and prevent the circulationof cells released into conduit 6 in the event of a catastrophic failureof the hollow fibers in BAL device 8. Bypass 12 provides a flow path forthe plasma if filter 9 becomes clogged or needs replacement.

Liver assist system 5 can also be used in a closed, off-line systemoperation, with reservoir bag 28 serving as the source of the plasmabeing introduced to the system. In this case, reservoir bag willgenerally be larger in size, for example, 2 liters.

Referring to the lower right inset of FIG. 1 and FIG. 3, a cellinoculation device 200 includes a flexible seeding bag 202 formed ofplastic (e.g. PVC) in which harvested liver cells to be inoculated inthe BAL device 8 are held. Cell inoculation device 200 includes an inlet212 through which cell suspension is dispensed within seeding bag 202and an outlet 206 which can be connected, for example, to an inlet tube60 of the liver assist system 5 (FIG. 1). Outlet 206 is connected to atube 208 which extends to the bottom portion of seeding bag 202 tomaximize the removal of cell suspension. The seeding bag 202 is easilyattached/detached from liver assist system 5 and is also a convenientreceptacle for transporting the cells.

The liver cells are removed from seeding bag 202 into BAL device 8 usinga pressure mechanism device 210 attached to cell inoculation device 200.In one embodiment, pressure mechanism device 210 may be a pressure cuffwhich is wrapped around seeding bag 202. Upon manual or automaticactuation, positive pressure is provided within the bag causing thecells to rise through tube 208 and out of outlet 206. In anotherembodiment, a pressurized gas source may be used to provide positivepressure via inlet hose 204 to the inside of the bag causing the cellsto rise through tube 208. In still a further embodiment, the cells canbe extracted from the bag by attaching a pump to outlet 206 of tube 208to pump the cells out of the bag.

A rinsing tube 214 is provided at the top of bag 202 for introducing arinsing solution (e.g., saline) to ensure the removal of residual cellsthat may settle within the bottom of bag.

Referring again to FIG. 1, liver assist system 5 includes bypassconduits which allow flexibility of use and ensure safety in case ofemergency. For example, the connection between the liver assist system 5and the plasma separation system 100 (or other external system) includestubing 70 which provides a path of flow for a portion of the treatedplasma back to plasma separation machine 100 from outlet 34 of reservoirbag 28. A bridge section 72 connects tubing 70 to tubing 74 whichintroduces the plasma to be treated to BAL device 8. When the plasmaseparation machine 100 is being used on-line with liver assist system 5,a pinch valve 76 is closed to prevent flow of plasma through bridgesection 72 so that all of the plasma returning along tubing 70 flows toplasma separation machine 100. In the event of an emergency, when itbecomes necessary to prevent interflow between the systems, pinch valves78, 80 are closed and pinch valve 76 is opened. In this arrangement,plasma from the plasma separation machine 100 can be made to flowthrough line 11, through open pinch valve 76, back to plasma separationmachine 100 through line 13. Line 15 may be open to a plasma storage bag47 within machine 100. Bag 47 may act as a compliant chamber to accountfor variations of the flow rate in and out of plasma separation machine100 through bypass 72. Pressure transducers 82, 84 are provided withinconduit 6 to sense extreme or inadequate levels of pressure. In thesesituations, signals from transducers 82, 84 are used to control pinchvalves 76, 78, 80 and pump 14, and may also be used to provide a visualor audible warning signal to alert the operator of the condition.Sampling ports may also be provided along conduit 6 to examine thecharacteristics of the plasma.

The liver assist system 5 provides the following features for rinsingand priming conduit 6 and its components (i.e., oxygenator, filters, andbioreactor unit). Tubing 92, 93, operating in conjunction with pinchvalves 94, 95, allows the introduction of two separate solutions forpriming and rinsing conduit 6 and the components disposed therein. Onesolution (e.g., saline) is introduced through tubing 92 with the othersolution (e.g., 5% dextrose) introduced through tubing 93. Bypasssegments allow for flushing the components independently or in series.The components may be rinsed and primed in any order.

Tubing 92, 93 for introducing priming solution and tubing 29, 113leading to integral waste bags 31, 33, 114 create a closed system andprovide an aseptic method of rinsing and priming the liver assist system5. In a preferred configuration, tubing 29, 92, 93 may be sealed andremoved to condense the liver assist system once it is ready to receiveplasma. The use of pinch valves 27 and 98 allows the priming solution tobe directed to waste bags 31, 33 after one pass before flowing to thewaste bags or recirculated through the liver assist system 5. The hollowfiber cartridge of the BAL device (without inoculated cells) is rinsedand primed along the fibers with the waste solution directed to wastebags 31, 33. A separate waste bag 114 is connected to BAL device 8 atin-port 61. The extra- capillary space between the bundle of fibers isprimed, and pores of the fibers are rinsed, with the waste solutiondirected to waste bag 114. When cleansing of BAL device 8 is complete,BAL device 8 is completely filled with saline and ready to receivecells.

Tubing 70, 74 between liver assist system 5 and the plasma separationmachine 100 is rinsed by opening valves 78, 80 for a period of time toallow some of the saline to flow through the tubing. It is generallyimportant that the liver assist system 5 be fully primed with thepriming solution at the initiation of plasma processing.

Liver cells from cell inoculation device 200 are then introduced atinlet 60 of BAL device 8 and the saline within the extra capillary spaceof the BAL device is displaced into waste bag 31, 33. Waste bags 31, 33,and 114 and lines 60 and 113 are then removed. In this condition, liverassist system 5 is considered to be primed and ready to receive plasma.

Other Embodiments

From the above description, one skilled in the art can easily ascertainthe essential characteristics of the present invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. For example, liver assist system 5, described above for useas an artificial liver, may be used in other medical applications.Moreover, the concept may be applicable to industrial operations. Thus,other embodiments are also within the claims.

What is claimed is:
 1. An apparatus for circulating and bioprocessing afluid, comprising:a conduit for circulating the fluid; an oxygenator,connected within said conduit, adapted to supply oxygen to the fluid; apump adapted to circulate the fluid through the conduit; a bioreactorunit, connected within said conduit, adapted to process the fluid; and acontainer, connected within said conduit, including:a first compartmentconfigured to receive the fluid into said container; an inlet connectedat a bottom end of said first compartment to provide the fluid into saidfirst compartment, the cross-sectional area of the first compartmentabruptly increasing from that of the cross-sectional area of the inlet;and a second compartment configured to receive fluid overflowing fromsaid first compartment; and an outlet connected to said secondcompartment to allow flow of the fluid out of said second container. 2.The apparatus of claim 1 further comprising an in-port connected withinthe conduit and configured to receive the fluid from an external system,and an out-port connected within the conduit and configured to return aportion of the processed fluid to the external system.
 3. The apparatusof claim 2 further comprising bypass structure which upon actuationprevents flow of the fluid between said conduit and the external system.4. The apparatus of claim 2 wherein the external system is a plasmaseparation apparatus.
 5. The apparatus of claim 4 further comprisingbypass structure which upon actuation prevents flow of the fluid betweensaid conduit and the external system.
 6. The apparatus of claim 5wherein the fluid from said in-port circulates through said bioreactorunit prior to being received by said container.
 7. The apparatus ofclaim 6 wherein said container includes a vent to allow the escape ofgas.
 8. The apparatus of claim 7 wherein said oxygenator is integrallyconnected to a heater adapted to maintain the fluid within a temperaturerange.
 9. The apparatus of claim 8 further comprising a filter,connected within said conduit, for filtering the fluid, wherein thefluid from said in-port circulates through said filter prior to beingreceived by said oxygenator and then by said bioreactor unit.
 10. Theapparatus of claim 2 wherein unprocessed fluid from said in-portcirculates through said bioreactor unit prior to being received by saidcontainer.
 11. The apparatus of claim 10 wherein said container includesa vent to allow the escape of gas.
 12. The apparatus of claim 1 whereinsaid oxygenator is integrally connected to a heater adapted to maintainthe fluid within a temperature range.
 13. The apparatus of claim 1further comprising a second in-port and a cell inoculation device forinoculating cells into said bioreactor unit, said inoculation deviceconnected to said second in-port and having:a receptacle with aninterior volume and an entrance for receiving cells into said interiorvolume; a pressure mechanism, attached to said receptacle, for providinga positive pressure within the interior volume of said receptacle withrespect to the external atmosphere of said receptacle to induce thewithdrawal of the cells from said receptacle; and a tube extending froman exit of said receptacle configured to allow the withdrawal of thecells from the interior volume.
 14. The apparatus of claim 1 whereinsaid container includes a vent to allow the escape of gas.
 15. Theapparatus of claim 1 further comprising a bypass conduit extendingaround the bioreactor unit.
 16. An apparatus for receiving a fluid froma plasma separation apparatus, circulating and bio-processing the fluid,and returning a portion of the fluid to the plasma separation apparatus,said apparatus comprising:a conduit for circulating the fluid; anin-port connected within said conduit and configured to receive thefluid from the plasma separation apparatus and an out-port configured toreturn a portion of the processed fluid to the plasma separationapparatus; an oxygenator, connected within said conduit, adapted tosupply oxygen to the fluid; a pump adapted to circulate the fluidthrough said conduit; a bioreactor unit, connected within said conduit,adapted to and process the fluid; a container connected within saidconduit adapted to receive the processed fluid from said bioreactor unitand release the processed fluid to said out-port, wherein said fluidcirculates through said bioreactor unit prior to being received by thecontainer; and bypass structure having an isolated section, said bypassstructure upon actuation isolating said conduit from the plasmaseparation apparatus so that fluid from the apparatus is allowed to flowthrough the conduit and fluid from the plasma separation apparatus isallowed to independently flow through the isolated section of the bypassstructure.
 17. The apparatus of claim 16 further comprising a secondin-port and a cell inoculation device for inoculating cells into saidbioreactor unit, said inoculation device connected to said in-port andhaving:a receptacle with an interior volume and an entrance forreceiving cells into said interior volume; a pressure mechanism,attached to said receptacle, for providing a positive pressure withinthe interior volume of said receptacle with respect to the externalatmosphere of said receptacle to induce the withdrawal of the cells fromsaid receptacle; and a tube extending from an exit of said receptacleconfigured to allow the withdrawal of the cells from the interiorvolume.
 18. The apparatus of claim 16 wherein said container includes avent to allow the escape of gas.
 19. The apparatus of claim 16 whereinsaid oxygenator is integrally connected to a heater adapted to maintainthe fluid within a temperature range.
 20. The apparatus of claim 16further comprising a filter, connected within said conduit, forfiltering the fluid, wherein the fluid from said in-port circulatesthrough said filter prior to being received by said oxygenator and thenby said bioreactor unit.
 21. The apparatus of claim 16 wherein thebypass structure includes a bridge section connected between the conduitand the isolated section.